One example of an axial flow rotary machine using an annular combustion chamber is a gas turbine engine for powering an aircraft. A flow path for working medium gases, typically air, extends axially through a compression section, a combustion section and a turbine section. The combustion section includes a combustion chamber. A plurality of nozzles are disposed in the combustion chamber for spraying fuel into the working medium flow path. The fuel is ignited and burned with oxygen in the working medium gases to add energy to the working medium gases.
The fuel system typically includes a source of pressurized fuel, such as fuel supplied from a fuel tank via a fuel control. The fuel control is responsive to power settings of the engine to vary the flow rate of fuel to the engine. A fuel distribution valve receives fuel from the fuel control and distributes the fuel via manifolds to the fuel nozzles in the combustion chamber. One example of such a fuel distribution valve is the fuel distribution valve used in the PW-4000 engine manufactured by the Pratt and Whitney Group, an operating unit of the Assignee of this invention. The fuel distribution valve for the PW-4000 engine includes a casing having a plurality of ports extending through the casing and a piston movable with respect to the ports for uncovering more or less area of the port in response to the flow rate of fuel.
Each port has the same amount of flow area for a given location of the piston to distribute an equal amount of fuel to the fuel nozzles in the combustion chamber. This provides uniform combustion within the combustion chamber and avoids localized high temperature regions in the chamber. These high temperature regions could cause overheating of components of the engine such as the turbine, which are downstream of the combustion chamber.
One of the problems encountered during operation of a gas turbine engine is that, at low fuel flow, the burning gases in the combustion chamber may blow out either as a result of high velocities of the working medium gases (primarily air) in the annular combustion chamber, low pressures or temperatures in the combustion chamber, a lean fuel/air ratio or combinations of these conditions which are aggravated by transient operation of the engine. As will be realized, a blowout of the combustion chamber will result in a loss of power from the engine and is a condition to be avoided.
Accordingly, scientists and engineers working under the direction of Applicants' Assignee have sought to improve the ability of the fuel supply system to resist a blowout of the combustion chamber during operative conditions of the engine.